When you create a Studio project using the New audiobook option and import a document that includes chapters, chapters will be automatically detected.
To manage chapters in an existing project, go to Project options in the top left corner, then select Manage chapters. This will open the Chapters sidebar.
You can add a new chapter using the + button. You can also rename and remove chapters using the Chapter actions (three dots) button, and drag and drop the chapters to rearrange them.